1. Preheat oven to 350° F (180° C). Line 12-cup muffin pan with paper cupcake liners; set aside.
2. Combine flours and baking powder in medium bowl; set aside.
Beat one margarine stick with granulated sugar in large bowl with electric mixer until creamy. Beat in eggs on low speed until blended, about 2 minutes. Beat in 1/2 cup (125 mL) milk and 1 tsp (5 ml) vanilla. Slowly beat in flour mixture just until combined, scraping sides of bowl occasionally. Evenly spoon batter into prepared pan.
3. Bake 25 minutes or until toothpick inserted in centers comes out clean. Cool in pan on wire rack 5 minutes. Remove cupcakes and cool completely.
4. Meanwhile, blend remaining margarine stick, icing sugar, remaining milk and remaining vanilla until blended. Beat on medium-high speed, scraping sides occasionally until light and fluffy, about 2 minutes. Evenly frost cooled cupcakes.